The present invention relates to a method and a system for measuring a flow rate of a fluid flowing within and through a pipe. More particularly, the invention is concerned with a flow rate measuring method and a system therefor with are capable of determining or measuring stably a mean flow rate of a fluid flowing through a pipe such as tube, conduit or the like in which distorted flows and disturbances such as turbulences may exist.
For measurement of flow rate of a fluid flowing within a pipe, there has heretofore been known a plural-sensor type flow meter system in which a plurality of detection elements (hereinafter referred to as the sensor) are disposed within the pipe and a single-sensor type flow meter system in which only one sensor is installed within the pipe.
As a typical plural-sensor type flow meter, there may be mentioned those disclosed in JU-A-61-1954188 and JP-A-61-120016, respectively. The first mentioned flow meter is based on the concept that the output signals of the individual sensors are integrated for determining stably an approximately true means (average) flow rate by using a calculating circuit of a corresponding structure notwithstanding of presence of distortions or deviations in the flow velocity (i.e. a distorted flow velocity distribution) brought about by geometrical factors (e.g. shapes) of an upstream pipe section, as is disclosed in JU-A-61-195418.
In the single-sensor type flow meter, a single hot wire element is installed within the pipe under tension in order to determine a curvilinear integral (line integral) of a flow velocity for thereby obtain a mean (average) flow rate, as disclosed in JP-A-54-125060.
The plural-sensor type flow meter in which a plurality of sensors are installed within the pipe suffers from a problem that when any one of the sensors is located in a region where flow disturbances due to vortexes, fluidal separations or the like brought about by geometry or shape of the pipe are significant, infinitesimal variations or fluctuations (fluidal noise) of the flow velocity are directly fetched by the mean flow calculating circuit as the input thereto, making it difficult or impossible to obtain the mean flow rate in a stable manner, because weights imparted to the outputs of the individual sensors are selected to be equal to one another or fixed.
The single-sensor type flow meter mentioned above also suffers the similar problem because no measures are taken against the influence of the infinitesimal variations in the flow velocity.
It is further noted that the location where the infinitesimal variation takes place in the fluid flow velocity is movable as a function of change in the distorted flow distribution profile or pattern. Consequently, the mean flow rate calculation using the fixed weight can not stably or consistently assure the availableness of accurate flow rate value by flexibly coping with the infinitesimal variation, giving rise to another problem.